Auto Complete feature in SAP

Dear all,
I just need to confirm , how can we make the auto-complete feature to become active , as i could not figure out how to do it . I mean to say , when i open SU01 or PFCG , and type any letter , it deos not bring the already used entries. Can you please guide me ,
Thanks

Hi Julie and David,
Thanks a lot, basically Low speed connection was checked , thats y i wasnt able to have those auto-complete. I have removed that check , and its working fine again..Thanks once again..Resolved
Regards,
Adnan